11/12/2013

eg technology ltd

What choices are available when designing casework for a Point of Care diagnostic device?

What choices are available when designing casework for a Point of Care diagnostic device?


First of all, let’s put aside considerations of style, aesthetics and company branding and focus on technical requirements. The first step we take with a client who wants to develop a point of care diagnostic instrument would be to determine a full requirements specification for the end device. The planned manufacturing volume, user interface, internal technology and construction, use environment, and, of course, budget, will all be primary factors in determining how the casework is designed and manufactured.


Volume of Manufacturing
If you are looking to produce a one-off proof-of-principle prototype then rapid prototyping (SLS, SLA or CNC machining) would give you an accurate representation of the final design in relatively short time scales without incurring tooling costs. The RIM (reaction injection moulding) process is ideal for producing robust casework parts with geometric freedom in low volumes (up to 1000’s) and is also suitable for much larger devices. RIM parts are sanded and painted which means there is a lot of freedom for secondary finishes. There are moderate up-front tooling costs but when considered over the product’s life cycle, these are generally very low. Sheet metal fabrication is also a good option for larger devices and has a low tooling cost but individual parts are more expensive. Therefore it is most suitable for volumes up to the hundreds and aesthetic options can be limited. Vacuum formed enclosures can be used in conjunction with sheet metal assemblies where more ergonomic or styled parts are required. Vacuum casting is another option for very low volumes (ten to thirty) but can be quite expensive and will always use a polyurethane, so material properties might not be exactly as required. Finally, injection moulding is the best cost option for volumes above 1000 and will result in very low part costs. However, as always with injection moulding, there will be high initial tooling costs and relatively strict design constraints.


User requirements
The design of your casework will of course depend on who will be using it and how. Aesthetics, use- prompts and labeling will all be determined by the end user, whether it is a doctor, lab technician or patient, and this will affect your casework design. User insight studies are highly recommended as they will help you understand issues such as whether access is needed in the enclosure for bulk fluids, consumables, or the removal of disposables and samples. They also enable assessment of the number of moving parts that you may need to consider ergonomically, and if screens or buttons are needed and where they should be placed. In terms of user interfaces, touch screens offer good versatility but have high costs involved in the software development and potential issues around cleaning and contamination. Membrane keypads are good solution for low volumes and simple operating requirements, and can offer great styling and branding opportunities. LCD displays are also a good option as they can be low cost with simple electronics and software. Additionally you will also need to consider assembly and serviceability and you may need to allow for the replacement of certain parts and modular upgrading.


Environment
The use environment will affect the design of your casework and influence the materials you use. Will it be used in a lab? If so, is it a cleanroom environment which will require the casework to be fully sealed and easily decontaminated? Do you need to consider anti-microbial resistant materials and the possible attack by solvents or agents used? The environment will also influence the size of your device (as will the internal technology). Consider the final location as the instrument may have to fit next to or interface with another instrument or existing equipment. If your device will be used outside the lab, and especially if it is handheld, robustness of your casework will also be a key factor.


Material and finishes
Manufacturing volumes will help determine the material you use but application and technology will determine the finishes you may require. The use environment may require anti-microbial finishes, or sealants to ensure cleanability (especially around any sample introduction ports), as well as anti-corrosion finishes to withstand associated chemicals. EMC (electro-magnetic compatibility) considerations are also important in material selection and in the case of polymer enclosures you may need to construct internal shields or apply metalised finishes to the inside surface to achieve compliance. You may also need to consider waterproofing and dust ingress (IP rating), heat management of internal components, and even fire risk, all of which will influence your choice of casework design and the materials and finishes you choose.